The provision of metallic effects in surface coatings, plastics coloration, cosmetic preparations and the like is well known. To achieve this effect, one approach has been to disperse both a metallic pigment and a transparent colored pigment in the composition. The metallic pigment is usually aluminum flake and the colored pigment can be, for instance, iron oxide. The art has also combined the two pigments into a single entity by precipitating the colored material on the aluminum flake.
The precipitation of, for instance, iron oxide on the aluminum flake was often carried out from an aqueous solution but that gave rise to various difficulties. Aluminum readily reacts in aqueous media, very dilute solutions of the iron oxide were required, complexing additives were necessary and the procedure had to be carried out in a limited pH range.
An alternate, non-aqueous procedure is described in U.S. Pat. No. 4,328,042. Here, iron pentacarbonyl is oxidized to iron oxide and carbon dioxide in a fluidized bed of the aluminum flake with oxygen at elevated temperature. To obtain reproducible results, the carbonyl cannot exceed 5 volume percent of the fluidizing gas. The use of the low concentration carbonyl and fluidized bed operation are obvious drawbacks of this approach.
It is desirable to provide a color effect material (CEM) which has the same or better pigment properties as the products just mentioned but without encountering the production and materials limitations of that prior art. The present invention is directed to satisfying that desire.
The present invention provides a color effect material (CEM) comprising a platelet-shaped substrate encapsulated with: (a) a highly light reflective first layer of, e.g., silver, gold, platinum, palladium, rhodium, ruthenium, osmium, iridium, or an alloy thereof; (b) a spacer layer of metal oxide, nitride, fluoride or carbide or polymer; whose refractive index is sufficiently high to minimize the incident angle dependent variable pathlength difference, in accordance with Snell""s Law, or thin enough to not be optically active; and optionally, (c) a light transparent layer which is either the same or a different metal as in the first layer or a spacer layer material different from that in the spacer layer and whose refractive index is higher than that of the spacer layer material. The CEM, where necessary, can be given a post-treatment for specific attributes such as weather stability, polymeric dispersability and cosmetic compatibility. The method of producing the CEM is also a part of this invention.